The digital image described by page description language may be interpreted and generated as actual page lattice data according to description of the image for storage or for a back-end output device to print and phototypeset etc., which is referred to as rasterization of the page digital image. The rasterization is a series of procedures including: parsing the original information such as width, height and bit depth etc.; processing the color of the image; processing transfer curves; and processing geometric transformation etc. After these procedures, the image is transferred from a user coordinate space to a device coordinate space, and the image is set to the page lattice of the device and thus the rasterization is done.
Since the conventional rasterization of the digital image results in higher output resolution and huge image, which occupy a lot of computer resources, intermediate files of image data (hereafter, image data intermediate files) needs to be often used. As shown in FIG. 1, the rasterizing process of the digital image may include steps of parsing the image data by an image data decoder and storing the image data in the image data intermediate files; and reading the data from the intermediate files by an image rasterizing processor and generating a final rasterized image lattice after processing the data.
The inventor recognized that the rasterization of the digital image has the following disadvantages: it needs to read from and write to disks for all the digital image data; and the color processor, Decode processor, the transfer curve processor and the image geometric transformation processor all read the image data intermediate files. Therefore, the amount of data to be read from and written to disks will increase a multiple of the square. In particular, in the case that the output resolution is relatively high, the operation with the huge amount of data seriously reduces processing efficiency. With improvement of operating efficiency of the back-end printing device, the rasterizing process becomes increasingly incompetent.